This invention relates generally to a semiconductor integrated circuit, and more particularly to a semiconductor integrated circuit effecting data security for and EEPROM (Electrically Erasable and Programmable Read Only Memory) in a microcomputer with a built-in EEPROM memory.
Among conventional microcomputers with a built-in EEPROM, a system capable of data security and disabling of the EEPROM thereby preventing the storing of a program by the operation from outside a semiconductor integrated circuit is known, such as with respect to the operation of the microcomputer announced by the Seeq Company in the ISSCC '83 in an article entitled "A 5 V Self-Adaptive Microcomputer With 16 Kb of E.sup.2 Program Storage and Security", by M. Bagula et al., published in the Digest of Technical Papers (IEEE-ISSCC Feb. 1983), on pages 34-35, wherein one of the registers in such a microcomputer is assigned as a data security EEPROM. Though easily operable, this sytem does not pay any consideration as to how to permanently maintain the EEPROM data.